Pressure transducers have been fabricated for operation at extremely high temperatures. In such transducers, one utilizes a metal diaphragm on the back of which is glassed a single network sensing element containing four piezoresistive strain gages. The gages are conventionally arranged in a Wheatstone bridge array. Upon the application of pressure, the diaphragm deflects slightly which induces strain onto the piezoresistors. The piezoresistors respond to this strain by a change of resistance. The four piezoresistors are arranged on the diaphragm such that two resistors are put in tension and the other two are placed in compression. This way, two resistors increase in value, while the others decrease in value by the same amount. This is well known. By connecting the two positive-going resistors on opposite arms of the Wheatstone bridge and doing likewise to the two negative-going resistors, the output of the Wheatstone bridge is a voltage which is proportional to the applied pressure. For high temperature operations, as indicated, the diaphragm is a metal diaphragm. See a co-pending application entitled High Temperature Pressure Transducer Employing Metal Diaphragm filed Jun. 15, 2006 as Ser. No. 11/453,445 for A. D. Kurtz et al, and assigned to Kulite Semiconductor Products, Inc., the assignee herein. In that application there is described a transducer utilizing a metal diaphragm and piezoresistors. The entire application is incorporated herein in its entirety. In regard to the above, the ratio or proportionality is known as the transducer sensitivity and is given by the following equation:
                    S        =                              1            P                    ⁢                                    V              OUT                                      V              B                                                          (        1        )            
S=Sensitivity
P=Applied Pressure
VOUT=Output Voltage
VB=Voltage applied to the bridge
It is highly desirable that the output of the pressure transducer is sensitive only to pressure and is not affected by other environmental factors. A notable factor is temperature and therefore the sensitivity of the pressure transducer should be independent of temperature. Many factors affect the sensitivity of a particular transducer, including geometric, physical and electrical factors. Unfortunately some of these factors are indeed temperature dependant which leads directly to temperature variation in the sensitivity. Various schemes must then be utilized to minimize this temperature variation of the sensitivity. These schemes are collectively known as temperature compensation. As one will ascertain, the prior art is replete with a number of temperature compensation methods. See for example U.S. Pat. No. 6,877,379 issued on Apr. 12, 2005 and entitled Doubly Compensated Pressure Transducer issued to A. D. Kurtz et al and assigned to the assignee herein. That patent describes a compensated pressure transducer which has coarse and fine temperature compensation. See also U.S. Pat. No. 6,700,473 issued on Mar. 2, 2004 entitled Pressure Transducer Employing On-Chip Resistor Compensation to A. D. Kurtz, et al and assigned to the assignee herein. That patent describes a technique for compensating temperature in a pressure transducer. Thus as one will ascertain, there are many techniques described in the prior art to provide compensation of pressure transducers for temperature. In regard to the present transducer as described above, one employs a pressure sensitive metal diaphragm with a piezoresistive Wheatstone bridge glassed directly to the back of the diaphragm. In such an arrangement, it has been shown that the predominant factor which affects the temperature variation of the sensitivity is the temperature variation of the metal's Modulus of Elasticity. Generally speaking, the Modulus of Elasticity for a substance is the ratio of stress to strain within the elastic range of the substance. This range is where Hooke's Law is obeyed. In particular, the Modulus of a metal decreases with increasing temperature. With a smaller Modulus, the same pressure applied to the metal diaphragm causes it to deflect further, which in turn causes increased strain applied to the Wheatstone bridge. Because of this effect, the sensitivity of the transducer increases with increasing temperature. Another way to state this is that the transducers temperature coefficient of sensitivity (TCS) is positive. This is in contrast with an integrated all silicon pressure transducer where the TCS is dominated not by mechanical factors, but rather by electrical effects of the piezoresistors themselves. Integrated all silicon pressure transducers typically have a negative TCS. To compensate the output versus pressure of a sensor with a negative TCS requires a bridge voltage that increases with increasing temperature. This is accomplished by placing a resistor with a zero temperature coefficient in series with the bridge. This compensation scheme is described in detail in U.S. Pat. No. 3,245,252 entitled Temperature Compensated Semiconductor Strain Gage Unit issued on Apr. 12, 1966 to A. D. Kurtz, et al. Of course the TCS of a metal diaphragm transducer is of opposite sign than an integrated all silicon pressure transducer and therefore a different compensation scheme must be employed. The prior art solution utilizes a temperature independent resistor placed in series with the Wheatstone bridge will not work in the case where TCS is positive because the zero coefficient series resistor causes an increase in the bridge voltage as the temperature increases. This is desirable when the TCS is negative, but exactly the opposite of what is needed when the TCS is positive as in the case for metal diaphragm resistor. Thus the present invention is concerned with a method of compensating the piezoresistive gage metal diaphragm pressure transducer.